Cationic polymerization as one or the primary processes for ionic polymerization has been widely applied for preparing many polymer materials, such as synthetic rubber, oil additives, plastic modifiers and the like. Since trace of impurities have an extremely great effect on the cationic polymerization process, the polymerization needs to be conducted under the conditions of almost no oxygen, no water and under protection with high purity inert gas. Taking the production of the typical industrial product of cationic polymerization-butyl rubber as an example, the polymerization needs to be conducted in the reaction medium of dry chloroalkane at a temperature as low as −100° C. Meanwhile, the water and oxygen content in the polymerization system should be strictly controlled to be several ppm or even lower to synthesize butyl rubber having high molecular weight. Thus the technological procedures of such polymerization are complicated, have strict requirements on the equipment and raw materials and have a high production cost. The current similar cationic polymerization system uses pure organic solvents as the reaction medium, and requires that the water content therein is lower than several ppm.
If water is used as the environmentally-friendly reaction medium for cationic polymerization, it may simplify the polymerization process, need less requirements on the equipments and reaction conditions, reduce the production cost and improve the heat transfer. Therefore, it has an important meaning to use an aqueous medium as the reaction medium for the cationic polymerization. In recent years, the cationic polymerization reaction using as the reaction medium an aqueous medium has aroused wide concern.
In 2006, Kostjuk S. V. and Ganachaud F. alleged in the thesis Cationic Polymerization of Styrene in Solution and Aqueous Suspension Using B(C6F5)3 as a Water-Tolerant Lewis Acid (Macromolecules, vol. 39) that B(C6F5)3 as a water-tolerant Lewis acid can successfully initiate the cationic polymerization of styrene in an aqueous phase medium. However, the resultant polystyrene has a lower molecular weight, the weight average molecular weight (Mw) thereof is about 3,000. Moreover, B(C6F5)3 is expensive (about ¥322/g) and is used in a large amount, and the molar ratio of B(C6F5)3 to monomers reaches 0.05.
In 2008, Kostjuk S. V., Radchenko A. V. and Ganachaud F. further mentioned in Controlled Cationic Polymerization of Cyclopentadiene with B(C6F5)3 as a Coinitiator in the Presence of Water (Journal of Polymer Science, Part A: Polymer Chemistry, vol. 46) that B(C6F5)3 may initiate the cationic polymerization of cyclopentadiene in an aqueous phase medium. However, the polymerization has a slow rate and needs to be conducted for scores of hours, and a conversion of less than 40% is just achieved. Moreover, only the polymer products having a low molecular weight (the Mw thereof is less than 2,500) can be obtained.
Similarly, Radchenko A. V., Kostjuk S. V. and Vasilenko I. V., et al disclosed in Controlled/living cationic polymerization of styrene with BF3·OEt2 as a coinitiator in the presence of water: Improvements and limitations (European Polymer Journal, Vol. 43, 2007) a process for cationic polymerization by initiating styrene with BF3·OEt2 in an organic reaction medium system having a low water concentration, i.e. water content being lower than 0.11 mol/L, wherein the resultant polymer has a lower molecular weight (the Mw, thereof is less than 2,000). Along with the slight increase of the water content, the polymerization rate will be obviously lowered; the molecular weight will be obviously decreased; the molecular weight distribution will be broadened. When the water content reaches 1.6 mol/L, i.e. water volume percent in the reaction medium being about 3.1%, the polymerization almost does not occur.
JP 10130315 and JP11080221 disclose a catonic polymerization of monomers with high reactivity, e.g. isobutylvinyl ether, p-methoxystyrene by using the Lewis acid, e.g. yttrium trifluorosulfonate or ytterbium trifluorosulfonate as an coiniator. However, only the polymer products having a low molecular weight (Mw<10,000) can be obtained. Moreover, yttrium trifluorosulfonate is expensive (about ¥140/g) and is used in a large amount, and the molar ratio of yttrium trifluorosulfonate to monomers reaches 0.05.
WO2004094486A1 and U.S. Pat. No. 7,202,371 respectively disclose a process for cationic polymerization of isoolefins in an aqueous reaction medium, wherein chelated diborane (e.g. C6F 4[B(C6F 5)2]2) and cumyl chloride are used respectively as the coinitiator and the initiator for initiating the cationic polymerization of isobutene at −60° C. in an aqueous reaction medium or copolymerization of isobutene with a small amount of isoprene. However, the prepared polymers still have a low molecular weight, and the maximum Mw is only 1.2×105, generally about 5×104, so that the polymers cannot be used as elastic materials. Moreover, the monomer polymerization conversion is also low. Among fourteen examples of cationic polymerization in an aqueous reaction medium listed in the present invention, the monomer polymerization conversion in twelve examples is lower than 50%. In addition, the chelated diborane compounds used in the process cannot be directly obtained by the commercial approaches. The chelated diborane compounds need to be prepared by a multi-step chemical reaction under the laboratory conditions, thereby increasing the complexity of the technological procedures. Moreover, the raw materials required for preparing such chelated diborane are expensive.
In conclusion, the prior art of cationic polymerization of vinyl monomer in the aqueous reaction medium is faced with many problems, such as high cost of initiating system, complex technological process, low polymerization efficiency, low molecular weight of polymer products and the like. Moreover, Lewis acids which have a high cost or are prepared specially are required as co-initiator. Thus the development of a new initiating system having a high activity, low cost, commercially obtainable raw materials and being easy and convenient to use in a polymerization process are the key points for solving the problems in cationic polymerization in the aqueous medium in the prior art, and can create conditions for simplifying the technological process, increasing the polymerization efficiency, synthesizing high molecular weight polymer products, reducing the cost and the like. However, the technologies and procedures of the cationic polymerization of the cationic-polymerizable monomers co-initiated directly by Lewis acid such as AlCl3, AlRCl2, BF3, TiCl4, FeCl3, SnCl4, ZnCl2 and the like in the aqueous medium or even a reaction medium which is totally water have not been reported yet.
Contents of the Invention
One object of the present invention is to provide an initiating system for cationic polymerization of cationic-polymerizable monomers, and a process for cationic polymerization of cationic-polymerizable monomers by using the initiating system, thereby overcoming one or more disadvantages in the prior art. In particular, one object of the present invention is to provide an initiating system for cationic polymerization of cationic-polymerizable monomers in an aqueous reaction medium, and a process for cationic polymerization of cationic-polymerizable monomers by using the initiating system in an aqueous reaction medium.
The technical solutions of the present invention include:
Embodiment 1: An initiating system for initiating a cationic polymerization in an aqueous reaction medium, wherein the initiating system comprises an initiator, an additive, a Lewis acid and an optional diluent.
Embodiment 2: The initiating system according to Embodiment 1, wherein the initiator is selected from the compounds which can provide protons, or from the group consisting of the organic tertiary alkyl or aralkyl functional compounds which can provide cationogens, or from the group consisting of the adducts of hydrogen halide and monomers, or mixtures of these substances, e.g. from the group consisting of the compounds which can provide protons and/or of the adducts of hydrogen halide and monomers.
Embodiment 3: The initiating system according to Embodiment 1 or 2, wherein Lewis acid is selected from one or more compounds having the general formula MXn or YRn-mXm, or mixtures thereof, wherein M is B, Al, Sn, Ti, Fe, Sb or Zn; X is F, Cl or Br; n is 2, 3, 4 or 5; m is 1,2 or 3; Y is Al, Sn, Ti or Zn; R is selected from the group consisting of alkyl, aryl, aralkyl, alkylaryl optionally substituted by halo substituents, wherein alkyl or alkyl in the alkyl-containing group is preferably C1-C20 alkyl, e.g. C1-C6 alkyl; aryl or aryl in the aryl-containing group is phenyl or naphthyl.
Embodiment 4. The initiating system according to any of Embodiments 1-3, wherein the additive is selected from the group consisting of organic compounds containing one or more heteroatoms, such as, nitrogen, oxygen, sulfur and phosphor, e.g. organic compounds containing one or more heteroatoms containing oxygen, sulfur and phosphor.
Embodiment 5. The initiating system according to any of Embodiments 1-4, wherein the additive is selected from the group consisting of the compounds containing one or more groups of —O—, —CO—, —COO—, —CON—, —S—, —SO—, —OSO—, —P—, —PO—, —PO3—, —PO4— and —PS—.
Embodiment 6. The initiating system according to any of Embodiments 1-5, wherein the molar ratio of the initiator, additive and Lewis acid is (5×104−25): (0.01-120):1, preferably (8×104−20): (0.02-100):1.
Embodiment 7. A polymerization system for cationic polymerization in an aqueous reaction medium, wherein the polymerization system consists of an initiating system according to any of Embodiments 1-6, one or more cationic-polymerizable monomers, an aqueous reaction medium and an optional dispersant, wherein the initiating system is in-situ formed in the polymerization system or mixed with other ingredients of the polymerization system after its preparation.
Embodiment 8. The polymerization system according to Embodiment 7, wherein the aqueous reaction medium further contains water-soluble compounds, such as ionic compounds and/or alcohols.
Embodiment 9. A process for polymerizing cationic-polymerizable monomers in an aqueous reaction medium, which comprises the step of polymerizing the polymerization system according to Embodiment 7 or 8.
Embodiment 10. A polymer prepared by the process according to Embodiment 9.